Maybe not the brightest thing for Bill to do, but this fear of encephalitis and West Nile was an overreaction.
At most they could have been a carrier for diseases among people in the room.
While unlikely, it is still possible, which is why it is unacceptable behavior by Gates. COMPLETELY unacceptable, and outrageous. People have enough concerns in their life already, without having to worry about some billionaire using them as a prop to make a point about disease. Gates contributions to the world have done a lot of good, but that doesn't give him the right to negatively impact if not possibly jeapordize the lives of ANYONE. Even if it was only mental trauma that they suffered, it was unnecessary, and abusive, and extremely arrogant of Gates to subject them to it, calling into question his supposed care for the well being of others, therefore destructive of his own reputation as well, making it all ultimately ignorant.